JP2010281287A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress oil dilution by appropriately setting stop, without fail, allowing temperature, in response to temperatures of an internal combustion engine and alcohol concentration in fuel. <P>SOLUTION: An ECU 60 executes engine stop control for temporarily stopping an internal combustion engine 10, when an engine temperature is a stop allowing temperature or higher. The stop allowing temperature is set lower as alcohol concentration in fuel is increased in a low temperature region and is set higher as alcohol concentration in fuel is increased in a high temperature region. Thus, opportunities for engine stop (EV operation) are increased in the low-temperature region so that engine drive operation and HV operation which are apt to increase in an oil dilution ratio can be avoided. In the high-temperature region, the engine drive operation and HV operation can be executed smoothly, while oil dilution ratio is suppressed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an internal combustion engine control device, and more particularly, to an internal combustion engine control device configured to perform engine stop control in an internal combustion engine using alcohol fuel.

  As a conventional technique, for example, as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2008-267227), an internal combustion engine control device configured to perform engine stop control is known. The engine stop control is a control for temporarily stopping the internal combustion engine when a predetermined stop condition is satisfied, for example, during idle operation or when the hybrid vehicle is running. This stop condition includes determination of whether or not the temperature of the internal combustion engine has exceeded a predetermined stop permission temperature. That is, in the engine stop control, the internal combustion engine is automatically stopped when the temperature of the internal combustion engine becomes higher than the stop permission temperature and another condition suitable for the engine stop control is satisfied.

  In the conventional technique, when the alcohol concentration in the fuel is high, the stop permission temperature is set high, and the execution frequency of the engine stop control is reduced. When the alcohol concentration in the fuel is high, the amount of alcohol mixed (oil diluted) from the injected fuel into the lubricating oil increases. Therefore, in this case, the internal combustion engine is kept at a high temperature by increasing the opportunity and duration of operation without performing engine stop control as much as possible. As a result, in the prior art, alcohol in the lubricating oil is evaporated at an early stage to suppress oil dilution.

JP 2008-267227 A

  By the way, in the conventional technology described above, when the alcohol concentration in the fuel is high, the stop permission temperature is set high, and the execution frequency of the engine stop control is reduced. However, depending on the temperature conditions, oil dilution is likely to proceed even if the alcohol concentration in the fuel is low. Even if the alcohol concentration in the fuel is high, it may be better to positively execute the engine stop control. For this reason, in the control of the prior art, the stop permission temperature may not necessarily be set appropriately, and there is a problem that oil dilution cannot be sufficiently suppressed.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to appropriately set a stop permission temperature in accordance with the temperature of the internal combustion engine and the alcohol concentration in the fuel, and perform oil dilution. It is an object of the present invention to provide a control device for an internal combustion engine that can reliably suppress the above.

A first invention is a fuel injection means for injecting fuel for combustion in a cylinder of an internal combustion engine;
Recirculation means for recirculating the evaporative gas of the diluted fuel, which is the injected fuel mixed in the lubricating oil of the internal combustion engine, to the intake system;
Engine stop control means for temporarily stopping the internal combustion engine when at least the temperature of the internal combustion engine becomes equal to or higher than a predetermined stop permission temperature;
Engine temperature acquisition means for acquiring a parameter corresponding to the temperature of the internal combustion engine or the wall temperature of the cylinder as the engine temperature;
Alcohol concentration acquisition means for acquiring a ratio of alcohol contained in the injected fuel as alcohol concentration;
When the engine temperature is equal to or lower than a predetermined reference temperature, a low temperature permission temperature variable means for setting the stop permission temperature lower as the alcohol concentration is higher,
When the engine temperature is higher than the reference temperature, high temperature permission temperature variable means for setting the stop permission temperature higher as the alcohol concentration is higher;
It is characterized by providing.

The second invention is an oil dilution rate acquisition means for acquiring a ratio of the diluted fuel mixed in the lubricating oil as an oil dilution rate;
Diluted fuel alcohol concentration acquisition means for acquiring a ratio of alcohol contained in the diluted fuel as a diluted fuel alcohol concentration;
An air-fuel ratio fluctuation determining means for determining whether or not the fluctuation of the air-fuel ratio caused by the recirculation of the evaporated gas falls within an allowable range based on at least the oil dilution ratio, the diluted fuel alcohol concentration, and the engine temperature;
An air-fuel ratio corresponding engine stop control means for stopping and operating the internal combustion engine based on the determination result of the air-fuel ratio fluctuation determination means;
It is set as the structure provided with.

  According to a third aspect of the invention, the diluted fuel alcohol concentration acquisition means is configured to calculate the diluted fuel alcohol concentration based on the engine temperature, the alcohol concentration in the injected fuel, the engine speed and the load.

The fourth invention comprises a dilution rate upper limit calculating means for calculating an upper limit value of the oil dilution rate corresponding to the allowable limit of the variation amount of the air-fuel ratio based on the engine temperature and the diluted fuel alcohol concentration,
The air-fuel ratio fluctuation determining means is configured to determine that the fluctuation of the air-fuel ratio falls within an allowable range when the actual oil dilution ratio acquired by the oil dilution ratio acquiring means is equal to or less than the upper limit value.

  According to a fifth aspect of the invention, there is provided an auxiliary power means capable of generating power for assisting the internal combustion engine.

  According to a sixth aspect of the invention, the fuel injection means is a direct injection type fuel injection valve that injects fuel into a cylinder of an internal combustion engine.

  According to the first invention, in the low temperature region where the engine temperature is equal to or lower than the reference temperature, the fuel injection amount increases as the alcohol concentration in the fuel increases, and the oil dilution amount tends to increase accordingly. For this reason, the low temperature permission temperature varying means sets the stop permission temperature lower as the alcohol concentration in the fuel is higher in the low temperature region, and increases the execution frequency of the engine stop control. As a result, in the low temperature region, it is possible to increase the chance of engine stop (EV operation), avoid engine drive operation and HV operation in which the oil dilution rate tends to increase, and suppress the oil dilution rate.

  On the other hand, in the high temperature region where the engine temperature is higher than the reference temperature, the alcohol in the injected fuel is likely to evaporate in the space and wall surface in the cylinder, so that the amount of injected fuel that contributes to oil dilution increases as the alcohol concentration increases. The oil dilution amount tends to decrease. For this reason, the high temperature permission temperature varying means increases the stop permission temperature as the alcohol concentration in the fuel is higher in the high temperature region (that is, the oil dilution rate is less likely to increase even when the internal combustion engine is operated). Set to reduce the frequency of engine stop control. Thereby, in the high temperature region, the engine drive operation and the HV operation can be smoothly performed while suppressing the oil dilution rate. Therefore, according to the first invention, it is possible to appropriately set the stop permission temperature corresponding to the change in the temperature state and the fuel property, in particular, considering the distillation characteristics of alcohol contained in the fuel, etc. The set value for the stop permission temperature can be finely controlled. As a result, the oil dilution rate can be constantly suppressed while ensuring the region in which the internal combustion engine can be operated as much as possible.

  According to the second aspect of the invention, the diluted fuel alcohol concentration is one of the factors that influence the fluctuation amount of the air-fuel ratio when the diluted fuel is returned to the intake system, but is not necessarily equal to the alcohol concentration in the injected fuel. . For this reason, the diluted fuel alcohol concentration acquisition means acquires the diluted fuel alcohol concentration, and the air-fuel ratio fluctuation determination means determines that the fluctuation of the air-fuel ratio is within an allowable range based on the diluted fuel alcohol concentration, the oil dilution rate, and the engine temperature. Judge whether it fits. Thereby, not only the oil dilution rate and the engine temperature but also the diluted fuel alcohol concentration can be reflected in the determination result of the air-fuel ratio fluctuation. That is, the determination accuracy can be increased as compared with the case where the diluted fuel alcohol concentration is not taken into consideration. Therefore, accurate control can be performed based on the determination result so that the fluctuation of the air-fuel ratio falls within the allowable range.

  According to the third invention, the diluted fuel alcohol concentration tends to decrease as the alcohol concentration in the injected fuel is higher and the engine temperature (in particular, the cylinder wall temperature) is higher. The oil dilution rate also changes depending on the fuel injection amount set based on the engine speed, the load, and the like, and the diluted fuel alcohol concentration also changes accordingly. Therefore, by diluting these characteristics in advance, the diluted fuel alcohol concentration acquisition means can calculate the diluted fuel alcohol concentration based on the engine temperature, the alcohol concentration in the injected fuel, the engine speed and the load. it can.

  According to the fourth invention, based on the oil dilution rate, the diluted fuel alcohol concentration, and the engine temperature, the amounts of the non-alcohol component and the alcohol component that evaporate from the lubricating oil after warm-up are calculated, respectively, and further returned to the intake system. The amount of each component can be calculated. Based on this calculation result and the excess air ratio (λ value) before and after dilution, the variation amount of the air-fuel ratio can be calculated. Therefore, if this procedure is calculated backward, the dilution rate upper limit calculating means can calculate the upper limit value of the oil dilution rate corresponding to the allowable limit of the air-fuel ratio fluctuation based on the engine temperature and the diluted fuel alcohol concentration. As a result, the air-fuel ratio fluctuation determining means can accurately and easily determine whether or not the fluctuation of the air-fuel ratio is acceptable only by comparing the actual oil dilution rate and the upper limit value.

  According to the fifth aspect of the present invention, for example, even when it is necessary to stop the internal combustion engine and reduce the oil dilution rate while the vehicle is traveling, it is possible to cope with the operation using the auxiliary power means, and the traveling state is Without being limited, the oil dilution rate can be controlled smoothly.

  According to the sixth invention, in an internal combustion engine using a direct injection type fuel injection valve, oil dilution is particularly likely to occur. Even in this case, according to the first to third inventions, the oil dilution rate can be stably suppressed.

It is a whole block diagram for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a characteristic diagram which shows the relationship between the fuel injection quantity of an internal combustion engine, and a fuel component. It is a characteristic diagram which shows the relationship between the temperature of an internal combustion engine, and an oil dilution rate about each of alcohol fuel and gasoline. It is a characteristic diagram which shows the relationship between the alcohol concentration in the injection fuel in a low temperature area | region, and stop permission temperature. It is a characteristic diagram which shows the relationship between the alcohol density | concentration in the injection fuel in a high temperature area | region, and stop permission temperature. In Embodiment 1 of this invention, it is a flowchart of the control performed by ECU. In Embodiment 1 of this invention, it is a flowchart of the control performed by ECU. In Embodiment 2 of this invention, it is a characteristic diagram which shows the relationship between engine temperature and dilution fuel alcohol density | concentration. It is a characteristic diagram which shows the distillation characteristic of a fuel. It is a characteristic diagram which shows the relationship between an oil dilution rate, injection fuel alcohol concentration, and dilution fuel alcohol concentration. In Embodiment 2 of this invention, it is a flowchart of the control performed by ECU.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
Hereinafter, Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is an overall configuration diagram for explaining a system configuration according to the first embodiment of the present invention. The system according to the present embodiment includes an internal combustion engine 10 including a direct injection engine that can use alcohol fuel, for example. Each cylinder 12 of the internal combustion engine 10 is provided with a combustion chamber 16 that expands and contracts by reciprocating movement of the piston 14. The piston 14 is connected to a crankshaft 18 that is an output shaft of the internal combustion engine 10.

  The internal combustion engine 10 also includes an intake passage 20 that sucks intake air into each cylinder 12 and an exhaust passage 22 that discharges exhaust gas from each cylinder 12. The intake passage 20 is provided with an air flow meter 24 for detecting the amount of intake air and an electronically controlled throttle valve 26. The throttle valve 26 is driven by a throttle motor 28 based on the accelerator opening and the like to increase or decrease the intake air amount. Each cylinder 12 of the internal combustion engine has a fuel injection valve 30 as a direct injection type fuel injection means for directly injecting fuel into the combustion chamber 16, and an ignition plug 32 for igniting an air-fuel mixture in the combustion chamber 16. An intake valve 34 for opening and closing the intake passage 20 with respect to the combustion chamber 16 and an exhaust valve 36 for opening and closing the exhaust passage 22 with respect to the combustion chamber 16 are provided.

  In addition, the internal combustion engine 10 includes a recirculation passage 40 as a recirculation means connected between the oil pan 38 and the intake passage 20. The recirculation passage 40 recirculates the evaporative gas of the diluted fuel mixed in the lubricating oil in the oil pan 38 to the intake system. In this case, the recirculation amount of the evaporative gas is configured to change according to the intake negative pressure.

  On the other hand, the system of the present embodiment includes a sensor system including a crank angle sensor 42, a water temperature sensor 44, an oil temperature sensor 46, an intake air temperature sensor 48, an alcohol sensor 50, etc., an electric motor 52 as auxiliary power means, and an internal combustion engine. An ECU (Electronic Control Unit) 60 for controlling the operating state of the engine 10 is provided. The crank angle sensor 42 outputs a signal synchronized with the rotation of the crankshaft 18, and the ECU 60 can detect the engine speed based on this output signal. The water temperature sensor 44 detects the temperature of the cooling water of the internal combustion engine, the oil temperature sensor 46 detects the temperature of the lubricating oil in the oil pan 38 (oil temperature), and the intake air temperature sensor 48 detects the temperature of the intake air (outside). Temperature).

  Furthermore, the alcohol sensor 50 constitutes the alcohol concentration acquisition means of the present embodiment, and detects the ratio of alcohol contained in the injected fuel as the alcohol concentration. In the present embodiment, the alcohol concentration is detected by the alcohol sensor 50. However, in the present invention, the alcohol concentration in the fuel is determined according to the operating state of the internal combustion engine without using the alcohol sensor 50. It is good also as a structure to estimate. In addition to the sensors described above, the sensor system includes various sensors necessary for controlling the vehicle and the internal combustion engine (for example, an accelerator opening sensor that detects an accelerator opening, an air-fuel ratio sensor that detects an air-fuel ratio of exhaust gas, etc. These sensors are connected to the input side of the ECU 60.

  Various actuators including a throttle motor 28, a fuel injection valve 30, a spark plug 32, and the like are connected to the output side of the ECU 60. The ECU 60 drives each actuator while detecting the operating state of the internal combustion engine using a sensor system. Specifically, the fuel injection amount, injection timing, ignition timing, and the like are set based on the output of the sensor system, and each actuator is driven in accordance with these settings. The operation control by the ECU 60 includes engine stop control and stop permission temperature variable control which will be described later.

  In the present embodiment, the internal combustion engine 10 is mounted on a vehicle such as a hybrid vehicle together with the electric motor 52. During the operation of the vehicle, the engine driving operation for stopping only the internal combustion engine 10 by stopping the electric motor 52, the HV operation for operating both the internal combustion engine 10 and the electric motor 52, and the internal combustion engine 10 are stopped. Thus, any one of the EV operations for operating only the electric motor 52 is selected according to the situation.

Next, engine stop control and stop permission temperature variable control executed by the ECU 60 will be described with reference to FIGS.
(Engine stop control)
The ECU 60 executes engine stop control for temporarily stopping the internal combustion engine 10 at a timing that does not require engine output, for example, in order to improve fuel economy performance, exhaust emission, and the like. Engine stop control includes idle stop control for stopping the engine during idle operation, EV operation for stopping the internal combustion engine and running the motor while the vehicle is running, and the like. In engine stop control, the internal combustion engine is automatically stopped when the temperature of the internal combustion engine (for example, cooling water temperature, lubricating oil temperature, etc.) is equal to or higher than the stop permission temperature and other stop conditions are satisfied. Let Here, the other stop condition is a condition for prohibiting the engine stop control in a situation where, for example, an engine stop causes a problem in vehicle performance.

  The stop permission temperature is variably set in order to adjust the execution frequency of the engine stop control according to the state of the vehicle or the internal combustion engine. For example, when the performance of in-vehicle equipment such as heating is insufficient, or when performing maximum warm-up in winter, it is desirable not to stop the internal combustion engine as much as possible. Is set to a higher temperature than normal. Further, in the stop permission temperature variable control described below, the stop permission temperature is variably set in order to suppress the oil dilution rate.

(Stop-permitted temperature variable control)
In general, in the direct injection type internal combustion engine 10, the amount of injected fuel adhering to the wall surface of the cylinder 12 increases. Therefore, a phenomenon that a part of this fuel dilutes the lubricating oil in the oil pan 38 (oil dilution) occurs. easy. The fuel (diluted fuel) mixed in the lubricating oil evaporates as the oil temperature rises and is returned to the combustion chamber 16 via the return passage 40. The diluted fuel evaporative gas causes fluctuations in the air-fuel ratio (A / F deviation). Therefore, in the stop permission temperature variable control, the amount of diluted fuel (oil dilution amount) contained in the lubricating oil is adjusted by controlling the stop permission temperature based on the engine temperature and the alcohol concentration in the fuel. / F deviation is suppressed.

  FIG. 2 is a characteristic diagram showing the relationship between the fuel injection amount and the fuel component of the internal combustion engine. In addition, in FIG. 2, the case where ethanol is used as alcohol is illustrated. As shown in FIG. 2, the fuel injection amount when using alcohol fuel increases as the alcohol concentration in the fuel increases. When the fuel injection amount increases, the amount of injected fuel adhering to the cylinder wall surface increases, so that the oil dilution amount also increases. However, the present inventor has found that the relationship between the alcohol concentration in the fuel and the amount of oil dilution varies depending on the temperature, as shown in FIG.

  FIG. 3 is a characteristic diagram showing the relationship between the temperature of the internal combustion engine (cooling water temperature) and the oil dilution rate for each of alcohol fuel and gasoline. Here, the oil dilution rate represents the amount (ratio) of diluted fuel contained in a certain amount of lubricating oil. In addition, “E0” in FIG. 3 indicates a gasoline-only fuel that does not include alcohol, and “E85” indicates a fuel that includes alcohol at a rate of 85 wt%. Similarly, “E20” and “E100” indicate a fuel having an alcohol concentration of 20 wt% and a fuel having an alcohol concentration of 100 wt% (alcohol only), respectively.

  As shown in FIG. 3, for example, with a temperature of about 10 ° C. as a reference temperature, there is a characteristic that the oil dilution ratio becomes higher as the alcohol concentration in the fuel is higher in a temperature region lower than the reference temperature. On the other hand, in the temperature range higher than the reference temperature, there is a characteristic that the oil dilution rate increases as the alcohol concentration decreases. This difference in characteristics is considered to be due to the following reason. First, since gasoline and alcohol in the fuel are difficult to evaporate at a low temperature, when the alcohol concentration in the fuel increases, the fuel injection amount increases accordingly, and the oil dilution amount also increases accordingly.

  On the other hand, when the temperature is high, the difference in fuel properties between alcohol and gasoline is strongly affected, and even if fuel with a high alcohol concentration is injected, the fuel itself adhering to the cylinder wall surface decreases. Moreover, since alcohol has a lower boiling point than gasoline, the alcohol in the injected fuel is likely to evaporate in the space and wall surface in the cylinder at high temperatures. For this reason, at the time of high temperature, as the alcohol concentration in the fuel increases, the amount of injected fuel that contributes to oil dilution decreases, and the oil dilution amount tends to decrease.

  Based on such characteristics, in the stop permission temperature variable control, the stop permission temperature is set based on the characteristic data shown in FIG. 4 when the engine temperature is in a low temperature region equal to or lower than the reference temperature. FIG. 4 is a characteristic diagram showing the relationship between the alcohol concentration in the injected fuel and the stop permission temperature in the low temperature region. As shown in this figure, in the low temperature region, the stop permission temperature is set lower as the alcohol concentration in the injected fuel is higher. As a result, the higher the alcohol concentration, the higher the execution frequency of the engine stop control. As a result, in the low temperature region, it is possible to increase the chance of engine stop (EV operation), avoid the engine drive operation and HV operation in which the oil dilution rate tends to increase, and reliably suppress the oil dilution rate. .

  Further, in the stop permission temperature variable control, the stop permission temperature is set based on the characteristic data shown in FIG. 5 when the engine temperature is in a high temperature region higher than the reference temperature. FIG. 5 is a characteristic diagram showing the relationship between the alcohol concentration in the injected fuel and the stop permission temperature in the high temperature region. As shown in this figure, in the high temperature region, the stop permission temperature is set higher as the alcohol concentration in the injected fuel is higher. Thereby, the higher the alcohol concentration (that is, the more difficult the oil dilution rate is to increase even when the internal combustion engine is operated), the lower the frequency of execution of engine stop control. As a result, in the high temperature region, the engine drive operation and the HV operation can be smoothly performed while suppressing the oil dilution rate. Note that the data shown in FIGS. 4 and 5 described above is stored in advance in the ECU 60 as map data, function expressions, or the like.

  In the above control, the engine temperature is an arbitrary parameter that reflects the temperature state of the internal combustion engine. For example, the temperature of the cooling water, the temperature of the lubricating oil, the wall temperature of the cylinder, and the like. The engine temperature used for the stop-permitted temperature variable control may be any of the water temperature, the oil temperature, and the cylinder wall temperature. However, since the alcohol in the injected fuel evaporates on the cylinder wall surface, the cylinder wall temperature is reduced. It is preferable to use it. Note that the cylinder wall temperature can be estimated from other engine temperatures by a method described later without being directly detected by a sensor or the like. In addition, the reference temperature that is the boundary between the low temperature region and the high temperature region is set to 10 ° C. as an example, but the present invention is not limited to this value, and the reference temperature depends on the characteristics of the fuel, the usage environment, and the like. Can be set to any value.

[Specific Processing for Realizing Embodiment 1]
6 and 7 are flowcharts of control executed by the ECU in the first embodiment of the present invention. The routines shown in these drawings are repeatedly executed during operation of the vehicle. First, specific processing for engine stop control will be described with reference to FIG. In the routine shown in FIG. 6, the ECU 60 first reads the operation information detected by the sensor system (step 100), and based on this operation information, the intake air amount, engine speed, cooling water temperature, oil temperature, intake air temperature, fuel The alcohol concentration, accelerator opening, exhaust air-fuel ratio, etc. are detected. Next, in step 102, it is determined whether or not the automatic stop is being performed, that is, whether or not the engine stop control is already being executed. When this determination is established, the routine proceeds to step 110 described later.

  If the determination in step 102 is not established, it is determined whether or not the engine temperature is equal to or higher than the stop permission temperature (step 104). This stop permission temperature is determined by a routine shown in FIG. When the determination in step 104 is satisfied, it is determined whether or not other stop conditions are satisfied (step 106). When this determination is also satisfied, the operation of the internal combustion engine is stopped (step 108). The engine stop in step 108 includes not only the case where the idling operation of the internal combustion engine is stopped but also the case where the EV operation is performed.

  On the other hand, when the determination in step 102 is satisfied, since the internal combustion engine is stopped, it is determined whether or not the automatic start condition is satisfied (step 110). When the determination at step 110 is satisfied, the internal combustion engine is restarted (step 112). Note that the restart of step 112 includes not only the case of restarting the engine drive operation but also the case of performing the HV operation.

  Next, a specific process of the stop permission temperature variable control will be described with reference to FIG. The routine shown in this figure is executed in parallel with the routine shown in FIG. In the routine shown in FIG. 7, first, the alcohol concentration in the fuel is calculated based on the detection signal of the alcohol sensor 50 (step 200). Further, the engine speed and the water temperature are detected based on the detection signals of the crank angle sensor 42 and the water temperature sensor 44 (step 202), and the engine load (load factor) is calculated based on the engine speed and the intake air amount (step 202). Step 204).

  Next, in step 206, the wall temperature of the cylinder 12 is calculated as the engine temperature. Specifically, the ECU 60 integrates the total amount of fuel injection injected after starting the internal combustion engine. The cylinder wall temperature rises from the starting temperature as the integrated value of the fuel injection amount (that is, the amount of heat generated in the cylinder 12) increases. However, when engine stop control is executed, Decreases accordingly. Therefore, the ECU 60 determines the current cylinder wall based on the integrated value of the fuel injection amount described above, the water temperature (or oil temperature) detected at the start, the temperature of the intake air, and the execution time when the engine stop control is executed. The temperature can be calculated.

  Next, in step 208, it is determined whether or not the cylinder wall temperature is higher than the reference temperature. When this determination is established, since the temperature is in the above-described high temperature region, the stop permission temperature is set based on the alcohol concentration / stop permission temperature map shown in FIG. 5 and the alcohol concentration in the fuel (step 210). On the other hand, when the determination in step 208 is not established, since it is a low temperature region, the stop permission temperature is set based on the alcohol concentration / stop permission temperature map shown in FIG. 4 and the alcohol concentration in the fuel (step 212).

  As described above in detail, according to the present embodiment, it is possible to appropriately set the stop permission temperature corresponding to the change in the temperature state and the fuel property, in particular, the distillation characteristics of alcohol contained in the fuel, etc. Considering this, the set value of the stop permission temperature can be finely controlled. Therefore, it is possible to constantly suppress the oil dilution rate while ensuring as much as possible a region where the internal combustion engine can be operated. In addition, when applied to a hybrid vehicle as in the present embodiment, for example, even when it is necessary to stop the internal combustion engine and reduce the oil dilution rate while the vehicle is running, it can be dealt with by EV operation. The oil dilution rate can be controlled smoothly without being restricted by the running state or the like.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS. In the present embodiment, the same system configuration as in the first embodiment (FIG. 1) is adopted, but in addition to the control contents of the first embodiment, control is performed based on the alcohol concentration in the diluted fuel. The configuration differs from that of the first embodiment in this respect. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Features of Embodiment 2]
The evaporative gas of the diluted fuel recirculated to the intake system causes the A / F shift. The A / F shift amount is not only the oil dilution rate but also the alcohol concentration in the diluted fuel (hereinafter, diluted fuel alcohol concentration). Also called). For this reason, in order to accurately predict the deviation amount of A / F, it is necessary to obtain the diluted fuel alcohol concentration. However, the diluted fuel alcohol concentration is often different from the alcohol concentration in the injected fuel (hereinafter referred to as the injected fuel alcohol concentration). That is, for example, even when fuel of E85 is injected, a part of the alcohol evaporates inside the cylinder or on the wall surface, so the diluted fuel alcohol concentration does not necessarily become a concentration equivalent to E85. Therefore, in the present embodiment, in order to predict the A / F deviation amount, first, the diluted fuel alcohol concentration is calculated. And it is the structure which determines whether the deviation | shift amount of A / F is settled in an allowable range based on at least oil dilution rate, diluted fuel alcohol concentration, and engine temperature (for example, oil temperature of lubricating oil).

(Calculation of diluted fuel alcohol concentration)
FIG. 8 is a characteristic diagram showing the relationship between engine temperature and diluted fuel alcohol concentration. This figure shows data when E85 is used as the fuel. As shown in FIG. 8, even if the alcohol concentration in the injected fuel is constant, the diluted fuel alcohol concentration decreases as the engine temperature (in particular, the cylinder wall temperature) increases. This can be derived from the fuel distillation characteristics shown in FIG. As shown in FIG. 9, for example, when fuel of E85 is injected, alcohol in the injected fuel remains in the cylinder even if the IN side wall temperature (the wall surface temperature of the cylinder at the lower position of the intake valve) is about 80 ° C. Evaporates almost 100% on the wall. Here, the state where the IN side wall temperature is 80 ° C. is a relatively low temperature state where the water temperature of the cooling water is about 40 ° C.

  Therefore, it can be seen that the alcohol in the injected fuel is less likely to become a diluted fuel as the engine temperature is higher. Further, the higher the injected fuel alcohol concentration, the lower the diluted fuel alcohol concentration due to the evaporation of alcohol. That is, the diluted fuel alcohol concentration tends to decrease as the injected fuel alcohol concentration increases and the engine temperature increases. With these characteristics, a characteristic diagram shown in FIG. 10 is derived.

  FIG. 10 is a characteristic diagram showing the relationship between the oil dilution rate, the injected fuel alcohol concentration, and the diluted fuel alcohol concentration. Here, FIG. 10A shows the relationship between the concentration of the injected fuel alcohol and the oil dilution rate when the engine temperature is 40 ° C., for example. FIG. 10B shows the ratio between the gasoline component and the alcohol component in the diluted fuel at a specific injected fuel alcohol concentration (that is, the diluted fuel alcohol concentration). The data shown in FIG. 10 is stored in advance in the ECU 60 as a plurality of types of map data corresponding to a plurality of engine temperatures, and FIG. 10 illustrates data when the engine temperature is 40 ° C. among these map data. Is. According to this map data, the oil dilution rate and the diluted fuel alcohol concentration can be calculated based on the engine temperature and the injected fuel alcohol concentration.

  FIG. 10 shows data corresponding to a fixed amount (unit amount) of fuel injection. The oil dilution rate and the diluted fuel alcohol concentration also change depending on the fuel injection amount. The fuel injection amount is set based on the engine speed and the load in normal fuel injection control. The ECU 60 also stores data for correcting the data in FIG. 10 according to the fuel injection amount (engine speed and load) in advance. Therefore, the ECU 60 can calculate the oil dilution rate and the diluted fuel alcohol concentration based on the engine temperature, the injected fuel alcohol concentration, the engine speed and the load.

(A / F deviation amount calculation)
Based on the oil dilution rate, diluted fuel alcohol concentration, and engine temperature described above, the amount of gasoline component and alcohol component evaporated from the lubricating oil after warm-up can be calculated. More specifically, if the gasoline component concentration in the diluted fuel gas is Ce0 and the alcohol component concentration in the diluted fuel gas is Ce100, these component concentrations Ce0 and Ce100 are the following (1), (2) It can be calculated by an equation. The fuel distillation coefficients Fve0 and Fve100 are obtained from the data shown in FIG. 9 and have a relationship of Fve100> Fve0.

Ce0 = fuel distillation coefficient Fve0 (oil temperature) x Σ gasoline dilution ratio (1)
Ce100 = Fuel distillation coefficient Fve100 (oil temperature) x Σ alcohol dilution ratio (2)

  Assuming that the amount of gasoline actually recirculated to the intake system (refluxed gasoline amount) and the amount of alcohol (refluxed alcohol amount) are Fe0 and Fe100, respectively, the recirculated gasoline amount Fe0 and the recirculated alcohol amount Fe100 are as follows: 3) and (4).

Fe0 = amount of recirculated gas per cycle x Ce0 (3)
Fe100 = recirculation gas amount in one cycle x Ce100 (4)

  Therefore, the deviation amount of A / F is calculated based on the excess air ratio (λ value) before and after dilution, and the reflux gasoline amount Fe0 and the reflux alcohol amount Fe100 obtained by the above formulas (3) and (4). Can do. In this case, the theoretical air-fuel ratio of gasoline is about 14.5, whereas the theoretical air-fuel ratio of alcohol (for example, ethanol) is about 9, so the degree of influence of each component on the A / F deviation is different. Therefore, the A / F deviation amount is calculated by correcting the difference in the influence of these components.

  By the above-described procedure, the A / F deviation amount can be calculated based on the oil dilution rate, the diluted fuel alcohol concentration, and the engine temperature. Therefore, if this procedure is calculated backward, the upper limit value of the oil dilution rate corresponding to the allowable limit of the A / F deviation amount can be calculated as the A / F deviation allowable dilution rate K. This A / F deviation allowable dilution rate K changes according to the diluted fuel alcohol concentration and the engine temperature. Accordingly, the ECU 60 stores in advance map data (oil temperature / diluted fuel alcohol concentration map) for calculating the A / F deviation allowable dilution rate K based on the diluted fuel alcohol concentration and the engine temperature. Then, the ECU 60 compares the oil dilution rate obtained during operation of the internal combustion engine with the A / F deviation allowable dilution rate K obtained from the map data, so that the A / F deviation amount is within the allowable range. It can be determined whether or not it fits.

[Specific Processing for Realizing Embodiment 2]
FIG. 11 is a flowchart of control executed by the ECU in the second embodiment of the present invention. The routine shown in this figure is performed in parallel with the control routine (FIGS. 6 and 7) according to the first embodiment. In the routine shown in FIG. 11, the ECU 60 first determines whether or not the automatic stop is being performed, that is, whether or not the engine stop control is already being executed. (Step 300).

  Next, in step 302, the fuel alcohol concentration is detected based on the detection signal from the alcohol sensor 50. In step 304, the engine speed and the coolant temperature are determined based on the detection signals from the crank angle sensor 42 and the water temperature sensor 44. Is detected. In step 306, the load is calculated based on the engine speed and the detection signal from the air flow meter 24. In step 308, the wall temperature of the cylinder is calculated by the same method as in step 206 of the first embodiment (FIG. 7).

  Next, in step 310, an oil dilution amount (hereinafter referred to as one cycle dilution amount) generated every time one combustion cycle (fuel injection) is performed in the cylinder is calculated. The one-cycle dilution amount is the amount of fuel mixed in the lubricating oil among the injected fuel injected at one time, and has a correlation with parameters such as the fuel injection amount, the injection timing, and the engine temperature. Therefore, by storing characteristic data representing these relationships in the ECU 60 in advance, the one-cycle dilution amount can be calculated based on the parameters.

  In step 312, as described above, the concentration of alcohol contained in the one-cycle dilution amount (hereinafter referred to as one-cycle dilution fuel alcohol concentration) based on the engine temperature, the injected fuel alcohol concentration, the engine speed and the load. ) Is calculated. That is, the ECU 60 can individually calculate the gasoline dilution amount generated every cycle and the alcohol dilution amount generated every cycle. Further, the ECU 60 stores data of the distillation characteristics shown in FIG. 9 and the like, and individually calculates the evaporation amount of gasoline and the evaporation amount of alcohol evaporated from the lubricating oil based on this data and the engine temperature. be able to.

  Next, in step 314, the integrated dilution rate and the diluted fuel alcohol concentration are calculated based on the one-cycle dilution amount, the one-cycle dilution fuel alcohol concentration, the gasoline evaporation amount, and the alcohol evaporation amount described above. That is, by integrating the one-cycle dilution amount for each combustion cycle of the cylinder and subtracting the evaporation amount of gasoline and alcohol from this integrated value, the integrated dilution rate that is the current oil dilution rate can be calculated. . Also, the current diluted fuel alcohol concentration is calculated by subtracting the alcohol evaporation amount from this integrated value while integrating the alcohol dilution amount obtained from the one-cycle diluted fuel alcohol concentration for each combustion cycle of the cylinder. Can do.

  Next, in step 316, the oil temperature of the lubricating oil is detected based on the detection signal of the oil temperature sensor 46. In the present invention, the oil temperature may be estimated by the following method without using the oil temperature sensor. In this method, first, the total amount of fuel injection injected after starting the internal combustion engine is integrated. Then, the oil temperature is estimated based on the integrated value of the fuel injection amount, the water temperature at the start, the temperature of the intake air, and the execution time when the engine stop control is executed. The oil temperature rises from the starting temperature as the integrated value of the fuel injection amount (the amount of heat generated in the cylinder 12) increases, and decreases according to the execution time of the engine stop control. Therefore, the ECU 60 can calculate the oil temperature by storing in advance data indicating the relationship between these parameters and the oil temperature.

  Next, in step 318, the A / F deviation allowable dilution rate K is calculated by referring to the aforementioned oil temperature / diluted fuel alcohol concentration map based on the current diluted fuel alcohol concentration and oil temperature. In step 320, it is determined whether or not the current integrated dilution rate is larger than the A / F deviation allowable dilution rate K. In the present embodiment, by calculating the A / F deviation allowable dilution ratio K, the air-fuel ratio fluctuation can be allowed only by comparing the actual oil dilution ratio and the A / F deviation allowable dilution ratio K. It can be determined accurately and easily. When the determination in step 320 is established, if the diluted fuel is recirculated to the intake system while the current oil dilution rate, diluted fuel alcohol concentration, and oil temperature are maintained, the deviation amount of A / F is out of the allowable range. There is a fear.

  Therefore, in this case, the internal combustion engine is stopped (step 322) and switched to the EV operation if necessary. Further, when the determination in step 320 is not established, it is determined that the A / F deviation amount is within the allowable range even if the diluted fuel is recirculated to the intake system. To maintain. On the other hand, since the internal combustion engine is stopped when the determination in step 300 is satisfied, the internal combustion engine is restarted when the automatic start condition is satisfied (steps 324 and 326).

  According to the present embodiment configured as described above, the following functions and effects can be obtained in addition to the functions and effects of the first embodiment. That is, in the present embodiment, not only the oil dilution rate and the engine temperature but also the diluted fuel alcohol concentration is reflected in the determination result of whether or not the deviation amount of A / F due to the reflux of the diluted fuel is acceptable. Can do. Thereby, compared with the case where the diluted fuel alcohol density | concentration is not considered, determination accuracy can be improved. Therefore, the internal combustion engine can be operated and stopped at an appropriate timing so that the A / F deviation amount falls within the allowable range, and the oil dilution rate can be accurately controlled.

  In the above embodiment, steps 100 to 108 in FIG. 6 show a specific example of the engine stop control means. In FIG. 7, step 206 is a specific example of the engine temperature acquisition means, step 200 is a specific example of the alcohol concentration acquisition means, step 210 is a specific example of the high temperature permission temperature variable means, and step 212 is the low temperature permission temperature variable means. Each specific example is shown. Further, in FIG. 11, step 308 is a specific example of engine temperature acquisition means, steps 310 and 314 are specific examples of oil dilution rate acquisition means, steps 312 and 314 are specific examples of diluted fuel alcohol concentration acquisition means, and step 318 is dilution. A specific example of the rate upper limit calculating means, step 320 shows a specific example of the air-fuel ratio fluctuation determining means, and steps 322 and 326 show specific examples of the air-fuel ratio corresponding engine stop control means.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 20 Intake passage 22 Exhaust passage 24 Air flow meter 26 Throttle valve 30 Fuel injection valve (fuel injection means)
32 Spark plug 34 Intake valve 36 Exhaust valve 38 Oil pan 40 Return passage (return means)
42 Crank angle sensor 44 Water temperature sensor 46 Oil temperature sensor 48 Intake air temperature sensor 50 Alcohol sensor (alcohol concentration acquisition means)
52 Electric motor (auxiliary power means)
60 ECU

Claims (6)

Fuel injection means for injecting fuel for combustion in a cylinder of an internal combustion engine;
Recirculation means for recirculating the evaporative gas of the diluted fuel, which is the injected fuel mixed in the lubricating oil of the internal combustion engine, to the intake system;
Engine stop control means for temporarily stopping the internal combustion engine when at least the temperature of the internal combustion engine becomes equal to or higher than a predetermined stop permission temperature;
Engine temperature acquisition means for acquiring a parameter corresponding to the temperature of the internal combustion engine or the wall temperature of the cylinder as the engine temperature;
Alcohol concentration acquisition means for acquiring a ratio of alcohol contained in the injected fuel as alcohol concentration;
When the engine temperature is equal to or lower than a predetermined reference temperature, a low temperature permission temperature variable means for setting the stop permission temperature lower as the alcohol concentration is higher,
When the engine temperature is higher than the reference temperature, high temperature permission temperature variable means for setting the stop permission temperature higher as the alcohol concentration is higher;
A control device for an internal combustion engine, comprising: Oil dilution rate acquisition means for acquiring a ratio of the diluted fuel mixed in the lubricating oil as an oil dilution rate;
Diluted fuel alcohol concentration acquisition means for acquiring a ratio of alcohol contained in the diluted fuel as a diluted fuel alcohol concentration;
An air-fuel ratio fluctuation determining means for determining whether or not the fluctuation of the air-fuel ratio caused by the recirculation of the evaporated gas falls within an allowable range based on at least the oil dilution ratio, the diluted fuel alcohol concentration, and the engine temperature;
An air-fuel ratio corresponding engine stop control means for stopping and operating the internal combustion engine based on the determination result of the air-fuel ratio fluctuation determination means;
The control device for an internal combustion engine according to claim 1, comprising:   The internal combustion engine according to claim 2, wherein the diluted fuel alcohol concentration acquisition means calculates the diluted fuel alcohol concentration based on the engine temperature, the alcohol concentration in the injected fuel, the engine speed and the load. Control device. A dilution rate upper limit calculating means for calculating an upper limit value of the oil dilution rate corresponding to the allowable limit of the variation amount of the air-fuel ratio based on the engine temperature and the diluted fuel alcohol concentration;
The air-fuel ratio fluctuation determining means is configured to determine that the fluctuation of the air-fuel ratio falls within an allowable range when the actual oil dilution ratio acquired by the oil dilution ratio acquiring means is less than or equal to the upper limit value. Item 4. The control device for an internal combustion engine according to Item 2 or 3.   The control apparatus for an internal combustion engine according to any one of claims 1 to 4, further comprising auxiliary power means capable of generating power for assisting the internal combustion engine.   The control device for an internal combustion engine according to any one of claims 1 to 5, wherein the fuel injection means is a direct injection type fuel injection valve that injects fuel into a cylinder of the internal combustion engine.

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